Low voltage d.c. motor



Feb. 8, 1966 R, A, SOMERS ETAL 3,234,417

Low VOLTAGE n.0. MOTOR Filed Nov. 24, 1961 Arrow/f7 United States Patent3,234,417 p LOW VOLTAGE D.C. MOTOR Raymond A. Somers, Fairfield, andRobert I. Tolmie,

Bridgeport, Conn., assignors to Sperry Rand Corporation, New York, N.Y.,a corporation of Delaware Filed Nov. 24, 15961, Ser. No. 154,579 20Claims.V (Cl. S10-154) The present invention relates to electricalmotors and more particularly to low voltage D.C. motors.

Many types of equipment demandlow voltage D.C. motors that are ruggedand reliable so that a minimum is expended in time and expense tomaintain.` the motors in proper operating condition. Some equipmentrequires, in addition, a compact motor but at no sacrifice in output.The foregoing requirements determined to a large extent the cost of themotors and ultimately the price to the user of the equipmentincorporating the motors. In certain equipment which may be categorizedas consumer products, such as electrical appliances, the price of themotor as yviewed by the producer of the equipment becomes a primaryconsideration. In other equipment Where the motor comprises but onecomponent of many and the cost thereof is little in comparison with theremainder of the equipment, price of the motor may not be of primaryimportance but yet is of consideration in ldetermining purchase, allother `.things being equal.

Manufacturers of electrical motors constantly strive to meet the aboverequirements but .generally are confronted with the usual problem ofproviding a motor which is attractive to the purchaser from thestandpoint of price. Ruggedness and reliability of the motor often timesdictate a motor design which is costly to manufacture viewed from thestandpoint of complexity of motor construction and/or expensivemanufacturing steps and involved assembly techniques.

In the manufacture and assembly of low voltage D.C. motors which employa permanent stator magnet or magnets substantially surrounding arotatable armature,

'the use of accurately ground magnets is required and the magnets mustbe assembled to `precision made structure to maintain proper gaptolerances between the rotor and the stator magnet or magnets, andbetween the yoke and the stator magnet. Of necessity, this requiresnumerous manufacturing steps both as regards the elements themselves andthe assembly o-f such elements to form the motor.- In addition, when acompact motor is desired the same may not be completely achievedinasmuch as the magnetic yoke must be sufficiently spaced from themagnets to reduce short-circuiting of magnetic flux through the yoke.

An object of the ,present invention is to provide a low voltage D.C.motor of novel construction.

Another object is to provide a novel loW voltage D.C. motor whereinsimplified assembly techniques are employed in the manufacture of themotor.

Still another object is to provide a low voltage D.C. motor whichemploys permanent stator magnets quickly assembled in close air gaptolerances with respect to the rotor.

A further object is to provide a low voltage D.C. motor wherein amagnetic return yoke or frame is employed with, the stator magnets andserves as a support for end bell structure without thev `requirement ofany threaded ice fastening means to maintain the rotor andv stator incornpletely assembled relationship.

A still further objecty is to'provide a novel low voltage D.C. motorwhich employs an adjustable yoke or frame to accommodate unground`stator magnets of varying dimensions.

Another object is to provide a low voltage D.C. motor which employs amagnetic yoke in contact with the stator magnets and maximum fluxdensity characteristics of the magnets are still maintained to effect. acompact motor.

Still another object is to provide a low voltage D.C. motor which ishighly eflicient, inexpensive, rugged, reliable, compact and consists ofa minimum number of parts.

The present invention therefore contemplates a low voltage D.C. motorwhich comprises a pair of spaced permanent stator magnets magnetized ina radial direction and having a rotor with windings disposed forrotation between the magnets. The shaft of the rotor is mounted forrotation in a pair of end bells or supports and the` latter includesspacer means which` engage. the arcuate surface of each magnet tomaintain a predetermined air gap between the arcuate surface of themagnet and the pole face of the rotor. A magnetic return yoke or frameembraces the stator magnets and is: adjustable to accommodate ungroundmagnets of varying dimensions. The frame serves to support the endbells, and in conjunction therewith, forms a housing `or casing ofbox-like configuration in which the frame has limited movement indirections vary-ing t-he transverse cross sectional area of the housing.

The above and other objects and advantages ofthe present invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein an embodiment of the invention is illustrated.

In the drawing wherein like reference characters refer to like partsthroughout the several views:

FIG. l is an elevational view, partly broken away, of a motor embodyingthe present invention;

FIG. 2 is a sectional view taken along the line 2 2 of FIG. l; f

FIG. 3 is a sectional view taken along the line 3-'3 of FIG. 2, and moreclearly shows the .positional relationship of the rotor and thepermanent magnets;

FIG. 4 is a transverse sectional view taken along the line 4 4 of FIG.1;

FIG. 5 is a view looking at the underside' of the motor as seen in FIG.1; f

FIG. 6 is a fragmentary view taken along the line 6--6 of FIG. 5 andshows in part commutator and brush arrangement of the motorrand FIG. 7is a partly sectional view showing the cornmutator structure,

Referring now to the drawing and particularly to FIGS. l and 2 hereoffor a more detailed description of the pre-sent invention, the referencecharacter 11 generally designates a motor `which comprises a rotor orarmature 13 having laminated armature segments 15, 17 and 19 (FIG. 4)symmetrically disposed about motor .output or armature shaft 21.Separate windings 23, 25 and 26 (shown only in FIG. 4) are provided forarmature segments 15, 17 and 19, respectively. The opposite ends ofshaft 21 are provided with bearing means 23' and 25' 3 which are seatedin end bells 27 and 29 respectively, the end bells being formed ofnon-magnetic material as for example, a plastic. A coil spring 31 isdisposed about shaft 21 and has one end in engagement with bearingmember 25' and its other end in contact with a commutator 33 to urge theshaft in an upward direction (as seen in FIG. 2) and against end bell27. Commutator 33 consists of three split conducting segments 35, 37 and39 (FIG. 7) which are electrically connected to windings 23, 25 and 26.The commutator segments are disposed on aninsert 41 `of insulatingmaterial as for example,

Bakelite, which is in turn press-litted to shaft 21. y

, End bells 27 and 29 are each provided with a project- "ing portion orannulus 43, preferably formed integral with the end bells, disposed inconcentric relationship with armature shaft 21. Each of the annuli 43 isprovvidedV with an inner surface45 and an outer surface 47, the latterextending radially beyond the armature segments for apredeterrnined'distance. Y

Motor 11 includes a pair of elongated permanent stator magnets 49 whichare'substantially rectangular in transverse cross-section except for oneside 51 thereof which isY substantially arcuate shaped; The remaininglongitudinally extending surfaces of magnet 49 designated as 53, 54 and55 (FIG. 4) areat or planar. Magnets 49 a're formed of a suitablematerial having high magnetic 'retentive properties as for' exampleBriumFerr'ite and are produced by a sintering or molding operation. A'magnetic return yoke V57 formed of suitable magnetic ma- `terial isprovided in contact Withvflat'surfacesfSS, 54 and v 55 of both magnets49. Frame 57 is substantially/'rectangular in transverse cross-sectionand comprises sep- -`arable L-shaped sections 59 and l61 having footportions 63 'and 65 FIG. 4) and leg portions 67 and 69 respectively.VUpper and lower apertures 71 and upper and lower apertures 73'areprovided in llegs 67 and 69 respectively, and are shaped to accommodatetherein I'radially extending lugs 75 formed on the upper and lowerfannuli'- 43. The horizontal dimensions of apertures 71 Aand-73 as seenin the drawing are greater than the horizontal dimensions of lugs 75 topermit lateral movement o f the frame sections 59 and 61 while thevertical dimensions of the apertures and of the lugs are substantiallythe samefto restrain` movement of sections`59 and 61 in di- ,rectionsnormal to end bells 27 and 29. Foot 65 of frame section 61is providedwith a tab 77 (FIGS. l and 4) which-is accommodated within a slot 79formed in leg 67 "of frame 4section 59 while a tab 81j is formed on legare provided on end bells 27 and 29 respectively and are ','disposedinwardly of these recesses 85 and' 87.. Lower end bell 29 has formedthereon a4 pair of diametrically i opposed depending posts (FIG. 5) eachof which accommodates a coiled b-rush retaining spring 92.' YOne end 93"of 'each spring 92 is straight and extends along the -external surfaceof end bell 29 to engage a commutator brush 93A disposed in a brushholder 94 formed integral with end -bell 29. Brush holder 94 is splitllongitudinally thereof (FIG. 6) to permit entry of end 93 of spring 92in engagement with brush 93A to maintain the latter in contact withcommutator 33. Substantially U-shaped flat spring terminals 95 each havearm portions extending into :brush holder 94 and. below and inengagement with brush 93A (FIG. 6) and constitutean input terminal forelectrically connecting motor 11 with a source of direct current energy.

One of the critical factors in the design and manufacx ture of motors isthe maintenance of a predetermined air gap between the rotor and thestator. Generally, it is desired to provide an air gap of minimumdimension in order to reduce the reluctance factor in the magneticcircuit to the smallest value possible. It may well be appreciated thatthis situation inherently poses no small problem in the manufacture ofthe motors inasmuch as the part-s constituting the rotor and the statorand their companion structure must be made Within exceedingly closetolerance. The foregoing requires expensive manufacturing steps inmachining or grinding the diiferent parts to the required dimensions inorder to maintain a minimum air gap. In addition, complex assemblyfixtures and testing procedures must be employed to assemble theprecision parts and to assure proper positional arrangement of thevarious elements, particularly those 0f` the rotor and the stator. v t

Low voltage D.C. motors have been proposed which employ a moldedpermanent stator magnet in the shape of a cylinder, and a magneticreturn yoke of similar shape engaging the outer surface of the magnet. Aproblemi Yconfronting the manufacturers of motors employing moldedcylindrical stator magnets is that as a result ofthe: molding processoften times the radial thickness'of the magnet will vary so thatextensive machiningv steps are required to grind the surfaces of themagnet to the deisigned dimensions. Moreover, the yoke must be precisionvground to the dimensions of the magnet and in addition,

.the magnet.

As indicated previously, magnets 49of the present invention are moldedand' such magnets also may be produced withdimensions which depart fromthe design dimensions. For example, in the molding of the magnets '49 itmay be found that dimensions designated asA,'B, Vand C (FIGS. 3 and 4)may vary and if it were necessary to contain the magnets within a fixedyoke or frame, extensive and expensive grinding operations'would' berequired. However, the present invention avoids machining operations onthe magnets by providing the adjustable lyoke or frame57 whichaccommodates magnets having variations in dimensions A, B, and `C. Anyvariations in the dimensions A and B merely entails movement of theseparable frame sections 59 and 61 in directions vreducing or increasingthe transverse cross-sectional area dened by the frame sections, theextent of movement of the frame sections being limited by the horizontaldimensionsof the apertures 71 and 73, slots 79 .and 83, .and shouldersS8 and 89. Moreover, vVariations in dimensionC, or the height of themagnet asseen in FIG. 3, are provided for by dimensioning the height ofthe frame 57 slightly in excess of what normally may be expected indimension C ofthe magnets, whereby a compensatory space exists 'betweenthe inner surfaces of end-bells'27 and 29 and the top .and bottom ofmagnets 49 (looking at FIG. 3). The construction of the presentinvention' should not be considered only from the standpoint ofaccommodating magnets having irregularV dimensions but shouldbeconsidered vadditionally as accommodating magnets of varying sizes andof configuration similar to magnets 49. As

long as su'ch different size magnets, fall within the limits determinedby apertures 71 and 73 and slots 79 and 83 they will be usable with thesubject construction.

It should be noted that regardless of variations in the dimensions A, Band-C of magnets 49 a predetermined air gap always will be maintainedbetween armature 13) and magnets 49 by -the structure of 'the presentinvention. If FIG. 3 of the drawing is' considered for example, it willbe seen that the outer surface 47 of annuli 43 engages. the innerarcuate surfaces 51 of magnets 49; Since annuli 43 are iixed withrespect to end bells 27 and 29 .and thus to the axis of shaft 21, theradial distanceofthe:

outer surface 47 from the center ofthe endbells`f27 and 29 willdetermine the dimension oftheA air gapbetweerr armature 13 and magnets49. In the assembly of' the: motor of `the present invention,framesections 59 and 61.

are pushed togetheruntil the arcuate sides 51 of magnets 49 engage, theouter surface 47 of annnli 43 so that in `every instance magnets 49 areAspaced a predetermined distance from the armature when the motor' 11 isfully assembled. In addition it should be noted that nonarcuatelongitudinal sides of the magnets are in engagement with the framesections.

Another `novel feature of .the present invention is that theconstruction of motor 11 provides for the yoke or frame 57 to be broughtinto contact` wit-h the permanent magnets 49 without causing any loss intlux by reason of such contact. This is accomplished bymagnetizingpermanent magnets 49 in such a manner that the magnetic lines of forceand the flux therein pass radiallfI through the magnets, as graphicallyshown bythe broken lines in FIG. 4. The ux internally of the magnetextends normal to the arcuate face 51 and passes across the air gap,through frame 57, thus completing the path for the magnetic circuit.This is contradistinction to permanent magnets which are magnetized in alongitudinal direction whereby the lines of force pass other than normalto the face of the rotor, or, if the construction of FIG. 4 isconsidered the lines of force would extend parallel to legs 67 and 69.It is apparent to those skilled in the art 4that if the structureof'FIG. 4 utilized longitudinal magnetization the portions of themagnets 49 adjacent to and in contact with the legs 67 and 69 of frame5,7` would be rendered substantially ineffective to maintain such fluxintensity inasmuch as the flux passing through such portions of magnets49.would be short-circuited to the frame without passing through thewindings. Consequently, the

radial magnetization of magnets 49 provides for a more compact motorinasmuch as a motor embodying magnets longitudinally magnetized wouldrequire spacing of the yoke from the magnets to eliminate theshort-circuiting problem, whereby the overall size of the motor wouldhave to be increased to provide for such spacing. On the other hand, themotor of the present invention could employ magnets longitudinallymagnetized although it is readily apparent that this would result in areduction in ux. One of the more importantl advantages of the presentAinvention is the novel construction of the motor 1i which permitsassembly and disassembly thereof with an absolute minimum of time andeffort. For example, except for assembly of armature 13, all of theelements of the motor may be assembled by hand. Thus, Vin the assemblyof the motor the opposite ends of shaft 21 are mounted in end bells 27and 29. Magnets 49 next are placedV between the end bells withthearcuate faces 51 in proximity to the annuli 43. One of the sections offrame S7 then is inserted between the end bells and .positioned so thatlugs 75 enter the apertures in the leg portion of'said section.Similarly, the second section of frame y lS7` is assembledwith the tabsand slots of the frame sections in registry. Finally, both sections 59and 61 may be grasped in one hand and pressed together whereby themagnets 49; will be in proper assembled relationship with the armature13 and frame 57 in contact with the magnets and seated on the end bells.`Disassembly of motor-11 may be accomplished just as simply byproceeding in reverse of the order of steps taken in assembly of themotor.

The adjustable yoke lor frame 574 has been illustrated and described ashaving two separable sections but it should be understood that it iswell within the contempla- I tion of the present invention for theframeV to consist of more than two sections as long as they function ina manner to achieve the desired results disclosed herein.

Although one lembodiment of the present invention has been illustratedand described in detail, it is to be expressly understood that theinvention is not limited thereto. Changes can be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as the same will now be understood by thoseskilled theart.

`air gap therebetween, anda frame having shaft.

What is claimed is:` f i `1. In an electric motor of the classdescribed, a rotatable armature including ashaft, means for mountingsaid shaft for rotation, a pair of permanent magnets supported inparallel relationship with said armature, spacing means bearing a fixed,relationship to the mountingy means and contactingeach magnet tomaintain a space between the magnets and the armature to'provide a`prede-termined air gap therebetween, and a frame. hYI-'lg Sidesdisposed inV planesl parallel tol the axis of rot-ation vof the shaft,`said frame surrounding and engagingthe m-agnetsfand being, adjustableto accomrnodauteY magnets of `vftllfyivllg dimensions. f

2. `In an electric motor of the class described, a pair of spacedpermanent magnets, a rotatable armaturefincluding a .shaft and disposedbetween said magnets, means mounting said shaft for rotation, spacermeans vbearing a fixed relationship to the mountingmeans land contactingeach magnet to space the magnets'from the' 4armature to provide apredetermined aii gap therebetween, and a frame having sides disposed inplanes parallel to the. axis of rotation of the shaft' and'sur-round-ingand engaging the `magnets, said frame being adjustable to accommodatemagnets of varying dimensions.l

3. In .an electric motor of the class. described, a pair of spacedpermanent magnets, a rotatable. armature includying a shaft and disposedbetween said magnets, means -mounting the shaft for rotation, spacermeansV carried, by 'said mounting means and contacting each magnetV tospace the magnets from the armature to provide a predetermined i s usides arranged in planes parallel to the. axis of rotation of saidsha-,ft and `surrounding and engaging said magnets, the sides of saidframe being adjustable -in directions transversely of *the4 axis ofrotation of the shaft to` accommodate magnets of varying dimensions.

4. The electric motor of claim 3, wherein means are lprovided on themounting.' means and` the frame to'allow limited movement of said frame,directions transversely of the axis of the shaft and to prevent movementof the sides of' said frame inl directions parallel tothe axis of the 5.In an electric motor ,of the class described, a pair of spaced permanentmagnets, a rotatable armature cluding a shaft and disposed between saidmagnets, a pair of support members mounting the shaft for rotation andsupporting said magnets, spacer means carried by the support members andengaging said magnetsr to Aspace the Vlatter from said Varrrra-ture toPYQVMide a predetermined air gap therebetween, and a frame surrdundingand `engaging said magnets and -in engagement with said support members,said frame bein-g adjustable to` accommodate magnets of varyingdimensions'. V

6. In an electric motor of the class. described, a pair of spacedpermanent magnets, a rotatable armature including a shaft and disposedbetween said magnets, a housing of boxfl-ike configuration enclosingsaid` magnets and said armature, said housing having airstA pair ofopposed and parallel walls mounting thev shaftforrotation and arrangedin planes extending normal tothe axis of rota-tion of the shaft, asecond and a third pair o f opposed and parallel Walls of said; 'housingengaging said magnets andbeilflg adjustable in direction transversely ofsaid shaft for accommodating magnetso-f varyingfdimensions, .and spacermeans` insaid housing` arranged to. conby said walls for engaging said'magnets and for spacing the magnets from the. armature; to provide aprede-termined air gap there'between, and the other walls of saidhousing being adjustable and movable relative to the rst mentioned pairof walls of said housing in direction extending transverselyf the shaft,said other walls engaging .themagnets and beingjmovable to vary thecross sectional .area of the housing in al plane transversely of the:shaftV to accommodate magnets of varying dimensions.

v 8. The motor of claim 7 wherein the spacer means lis rformedintegrally with'the rst mentioned pair of housing Walls and extendsbetween the magnets and .the shaft.

9. The motor of claim 7 wherein 4the spacer means comprises an annularprojecting portion formed on each of the first mentioned pair of housingwalls and are con- 'centrically disposed with respect to the shaft, andsaid `ma'gnetsare each provided with an arcuate face engaged by saidannular portion. Y 10. The motor of claim 7 wherein means are providedon saidihousingwalls to prevent relative movement therebetween inadirection extending longitudinally of the shaft but provides limitedmovement of said other walls relative toV said rst pair ofwalls indirections extending `transversely of said shaft.'

11.y In an electric motor of the class described, a frame of rectangularcross-section having .two pairs of oppositely v disposed walls Vand openat two sides, the walls of said frame being movable in directionsextending transversely -to the planes'thereof to vary the crosssectional area of Vthe frame, a pair of cover members substantiallyrectangular in shape Vcovering the open sides of Ithe frame and engagingthe'edges of the Wall in said frame at the open sides thereof, arecessed portion formed in `ea'ch'of said cover members to accommodatethe edges of said frame walls engaging said `cover members, "a shoulderformed in said recessed portions ,for limiting movement of the framewalls in directions reducing the cross sectional area of the" frame,.'a` rotatablel armature including a shaft mounted for rotation in saidcover members with the axis ofrotation extending normall'to the covermembers, a pa-ir of permanent magnets arranged between the arma- -ture.andthe walls of the frame, said magnets being engaged by thewallsfrofsaid frame, and a spacer 'member ,oneach cover memberpextending betweenthe magnets vpredetermined air gap between said-magnets and said Yarmature.

andthe shaft and engaging. the magnets to main-tain a 12. The electricmotor claim llrwherein the frame comprises -a ,pair of L-shaped membersprovided with cooperating tongues and slots to provide for interlockingengagement of said members.

13. Thev electric Ymotor of claim 12 wherein the longer sides of theL-.shaped members are provided with aperptures, and the cover` membersare provided with ngers for accommodation within said apertures toArestrain movet ,ment of said L-'shaped members relative to the coverYmembers in directions longitudinally'ofthe shaft.

14. Inan'electric ymotor -of the"class described, a ro- "tatahlegarmature `having a shaft, meansmountingsaid tshaft for rotation, apairof spaced permanent "magnets polygonal-shaped' in transverse crosssections, each of l said magnets having iirstandv second pairs of spacedand parallelside walls, said first pairof side walls of each magincoaxial relationship withv said shaft,-said magnets being magnetized indirections normal to the inner pole faces, fa magnetic return framesurrounding and engaging the non-arcuate side walls of said Ifirst andsecond pair of side walls of said magnets,'.and spacer means engagingthe inner pole faces vof said magnets' to maintain a predeterminedair-"gaprbetweensaidmagnets and' said'a'rmature.

15. In an electric motor of the class described, a ro- CII tatablearmature having a shaft, a pair of opposed and lspaced support membersmounting said shaft for rotation about an axis perpendicular to saidsupport members, a pair of spaced permanent magnets substantially rec--tangular in transverse cross section except for one concave arcuateside, said arcuate sides providing inner arcuate pole faces disposed incoaxial relationship with said shaft, the remaining sides of each ofsaid magnets comprising non-arcuate outer pole faces, said magnets beingmagnetized in directions normal to the inner arcuate pole faces, amagnetic return frame having two pairs of parallel and opposed sidesextending in planes parallel to said shaft and arranged between saidsupport members, said magnetic return frame being in engagement with thenon-arcuate pole faces of said magnets, and spacer means engaging theinner pole faces of said ,magnets to maintain a predetermined air gapbetween the 'inn-er pole faces of said magnets and said armature.

16. The electric motor of claim 1S wherein said spacer means are carriedby said support members and comprise annular shaped members arrangedcoaxial with the shaft, said annular shaped members having outersurfaces disposed in concentric relationship with the inner pole facesof said magnets and in contact therewith.

17. In an electric motor of the class described, a pair of spacedelongatedv permanent magnets substantially rectangular in transversecross section except for one side thereof being arcuate shaped, saidmagnets being magnetized in directions normal to the arcuate sides andthe latter being disposed along a surface of revolution about a commoncenter, a rotatable armature having a shaft arranged with its axis ofrotation coincident with said common center, said armature beingdisposed in spaced concentric relationship with the inner sides of saidmagnets, a pair of spaced support members mounting the shaft forrotation, said support members arranged at opposed ends of said magnetsand extending in planes lying transversely of the magnets, a magneticreturn rectangularshaped frame arranged between said support members andin engagement therewith, said magnetic return frame surrounding andengaging the non-arcuate sides of said magnets, and an annular spacermember carried by each support member concentric with said shaft andhaving an outer surface in contact withY the arcuate sides of saidmagnets to maintain a predetermined air gap between the arcuate sides ofsaid magnets and said armature.

18. In an electric motor of the class described, a housing ofrectangular cross section including side walls and a pair of spaced endwalls extending transversely of the side walls, a rotatable armatureincluding a shaft journaled for rotation in said end walls and havingits axis of rotation extending normal to the latter and parallel withsaid side walls, spacer means carried by said end Walls and spaced fromsaidside walls, and a pair of spaced permanent magnets disposed betweensaid spacer means and the side walls of said housing in spacedrelationship with said armature, each of said permanent magnets havingan inner pole face adjacent to the armature and engagedby said spacermeans to maintain a predetermined air gap between said armature and saidinner pole face.

19. The electric motor of claim 18 wherein the spacer means are formedintegral with the end walls and extend into the housing between saidside walls and the shaft of said armature.

20. In an electric motor of the class described, a frame of rectangularcross section having spaced andparallel lateral walls with a pair ofopen sides in planes extending normal to said lateral walls, a rotatablearmature having a shaft extendingin directions perpendicular` to theplanes containing the open -sides of said frame, a pair of spacedpermanent magnets having inner pole faces disposed about said armatureand outer pole faces in engagement with the lateral walls of said frame,and a pair of spaced cover members disposed in the planes of the opensides of said frame and seating the edges of said'la'teral'wallsthereon,

said cover members mounting said shaft for rotation and engaging theinner pole faces of said magnets to maintain the magnets in spacedrelationship with said armature to provide a predetermined air gapbetween the inner pole faces of said magnets and said armature.

References Cited by the Examiner UNITED STATES PATENTS 2,325,915 8/1943Naul. 2,479,455

1 0 2,482,875 9/ 1949 Sawyer 310-154 2,617,851 11/1952 Bisch 310-1542,935,785 5/1960 Stein 310--154 2,939,024 5 1960 Mabuchi.

FOREIGN PATENTS 1,220,515 5/ 1960 France.

781,107 8/ 1957 Great Britain.

ORIS L. RADER, Primary Examiner.

8/1949 Aronoi 310-154 10 MILTON O. HIRSHFIELD, Examiner.

1. IN AN ELECTRIC MOTOR OF THE CLASS DESCRIBED, A ROTATABLE ARMATUREINCLUDING A SHAFT, MEANS FOR MOUNTING SAID SHAFT FOR ROTATION, A PAIR OFPERMANENT MAGNETS SUPPORTED IN PARALLEL RELATIONSHIP WITH SAID ARMATURE,SPACING MEANS BEARING A FIXED RELATIONSHIP TO THE MOUNTING MEANS ANDCONTACTING EACH MAGNET TO MAINTAIN A SPACE BETWEEN THE MAGNETS AND THEARMATURE TO PROVIDE A PREDETERMINED AIR GAP THEREBETWEEN, AND A FRAMEHAVING SIDES DISPOSED IN PLANES PARALLEL TO THE AXIS OF ROTATION OF THESHAFT, SAID FRAME SURROUNDING AND ENGAGING THE MAGNETS AND BEINGADJUSTABLE TO ACCOMODATE MAGNETS OF VARYING DIMENSIONS.